Field of the Invention
The present invention relates to a foldable display device and a method of manufacturing the same. More particularly, the present invention relates to a foldable display device with improved reliability.
Discussion of the Related Art
As information technology and mobile communication technology have been developed, a display device being capable of displaying a visual image has also been developed. Flat panel display devices, such as a liquid crystal display (LCD) device and an organic light emitting display (OLED) device, are developed and used.
In general, an LCD device includes a liquid crystal panel, which includes upper and lower substrates and a liquid crystal layer therebetween. The liquid crystal layer is driven by an electric field induced between a pixel electrode and a common electrode to display images.
An OLED device includes an organic emitting diode which includes an anode, a cathode and an organic emitting layer therebetween. In the organic emitting diode, holes and electrodes respectively from the anode and the cathode are combined such that light is emitted from the organic emitting layer to display images.
Recently, a foldable display device, which is fabricated by using a flexible substrate, is in demand. The foldable display device is folded to be portable and is unfolded to display images. Namely, with the foldable display device, a large-sized image display can be provided, and portability of the display device is improved.
FIG. 1 is a schematic cross-sectional view of a foldable display device according to the related art.
As shown in FIG. 1, the foldable display device 10 includes a display panel 20, a backplate 30 and a cover window 40.
The display panel 20 includes a flexible substrate 22, a display part 24 on the flexible substrate 22. For example, the flexible substrate 22 may be a polyimide substrate.
When the display panel 20 is an organic emitting diode panel, the display part 24 may include an organic emitting diode and a thin film transistor (TFT) for driving the organic emitting diode. The organic emitting diode may include an anode, which is connected to the TFT, an organic emitting layer on the anode, and a cathode on the organic emitting layer. In addition, an encapsulation film for preventing moisture penetration may cover the organic emitting diode.
On the other hand, when the display panel 20 is a liquid crystal panel, the display part 24 may include a thin film transistor (TFT) on the flexible substrate 22, a pixel electrode, which is connected to the TFT, a counter substrate, which faces the flexible substrate 22, a common electrode, which is on the flexible substrate 22 or the counter substrate, and a liquid crystal layer between the flexible substrate 22 and the counter substrate. The display panel 20 may further include a backlight unit.
With a carrier substrate (not shown) attached to a lower surface of the flexible substrate 22, elements such as the TFT are formed on the flexible substrate 22, and the carrier substrate is released to obtain the flexible display panel 20.
In the flexible display panel 20, since the flexible substrate 22 is thin, the backplate 30 for supporting the display panel 20 is disposed under the flexible substrate 22. For example, the backplate 30 may be formed of polyethylene terephthalate (PET) and may be attached to the display panel 20 by an adhesive layer 32.
The cover window 40 is attached to an upper side of the display panel 20. The damage on the display panel 20 from outer impacts is prevented by the cover window 40. Although not shown, the cover window 40 may be attached to the display panel 20 by an adhesive layer.
In the related art foldable display device, the PET film having about 100 micrometers is used for the backplate 30. When the folding and unfolding operation is repeated in the foldable display device 10, plastic deformation occurs in the backplate 30 such that the restoration of the folded display device to its original configuration may become difficult.
Namely, as shown in FIGS. 2A and 2B, since there is a plastic deformation problem in the backplate 30 (of FIG. 1) of the PET film, there may be limitations in the folding and unfolding operation of the foldable display device 10. Namely, the folding and unfolding characteristics of the foldable display device 10 deteriorate. FIG. 2A illustrates that the backplate 30 is deformed and does not revert to its original shape when external force is removed. In FIG. 2B shows a result of plastic deformation of the backplate 30 after a repeated folding and unfolding where a center portion is plastic deformed downward and two wing portions are plastic deformed upward.
By reducing a thickness of the backplate 30, the plastic deformation problem in the backplate 30 may be decreased. However, the elastic restoring energy of the backplate 30 having such a reduced thickness may be decreased and the time for restoring the folded display device to its original state may also be increased.